Voters are set to cast their ballots in three Western states next month on whether to legalize the sale of marijuana for recreational use, initiatives that would directly violate federal law but that have drawn only silence from the Justice Department.

Despite the urging of drug enforcement experts, officials in Washington have not said how the federal government would deal with possible state laws in Colorado, Washington and Oregon that would conflict with the federal Controlled Substances Act. Federal law prohibits the production, possession and sale of marijuana and classifies marijuana as a Schedule 1 drug, putting it in the same category as LSD and heroin.

Nine former administrators of the Drug Enforcement Administration wrote a letter last month to Attorney General Eric H. Holder Jr., urging him to publicly oppose the ballot initiatives that, if passed, would make the states the first in the nation to decriminalize marijuana for recreational use by adults.

“To continue to remain silent conveys to the American public and the global community a tacit acceptance of these dangerous initiatives,” wrote the former administrators, who oversaw the DEA under both Democratic and Republican presidents from 1973 to 2007. “We urge you to take a public position on these initiatives as soon as possible.”

Holder has not responded to the letter. The former officials are planning to hold a news conference Monday to press their concerns more publicly.

“The Justice Department should speak out ahead of the ballot initiatives to avoid immediate court action,” said Peter Bensinger, the DEA administrator from 1976 to 1981. “The initiatives will be in direct conflict with federal law, international treaty obligations and Supreme Court rulings.”

The Justice Department can file suit to try to block state laws that it deems to have violated federal statutes. It did that, for example, after Arizona passed a law in 2010 that the state said was aimed at cracking down on illegal immigrants but that the Obama administration believed was unconstitutional. In other cases, officials have simply made the Justice Department’s stance clear ahead of ballot initiatives, as Holder did in 2010 when he said that officials opposed a California measure to legalize marijuana.

But with the upcoming initiatives over legalization, Justice Department spokeswoman Allison W. Price said the department would not comment. “We are not going to speculate on the outcome of various ballot initiatives state by state,” she said.

Colorado’s measure, known as Amendment 64, is the most likely to pass, according to observers and local polls. Under the measure, retail stores would be allowed to sell marijuana, and it would be taxed and regulated like tobacco and alcohol.

Growing operations would be legalized, as would “infusion factories” that could blend marijuana into brownies, candy bars and lollipops, according to Tom Gorman, the director of the federal Rocky Mountain High-Intensity Drug Trafficking Area.

“If this passes, Colorado would have the most liberal marijuana laws in the developed world, more liberal than the Netherlands,” said Gorman, whose group brings together local, state and federal law enforcement officials. “It’s illegal for a state to pass a constitutional measure that allows its citizens to violate federal law.”

The initiative has the support of 51 percent of state voters, according to a poll conducted for the Denver Post. More than 300 physicians in the state have joined the campaign for legalization.

“As physicians, we have a professional obligation to do no harm,” Bruce Madison, former associate medical director of the faculty at the University of Colorado School of Medicine, said in a statement. “But the truth is that the Colorado marijuana laws do just that, by wasting hundreds of millions of dollars in a failed war on marijuana, by ruining thousands of lives by unnecessary arrest and incarceration, and by causing the deaths of hundreds of people killed in black-market criminal activities.”

In a letter to President Obama, four former White House drug czars said the administration’s “non-discussion” stance “is sending a message that you and your administration are indifferent to the legalization issue.”

“We stand united against any efforts . . .to legalize marijuana or any other currently illegal substances and urge you to respond . . .expressing unequivocal opposition to marijuana legalization generally and these initiatives specifically,” the former National Drug Control Policy directors wrote.

Along with the Colorado ballot proposal, Initiative 502 in Washington and Measure 80 in Oregon would allow people who are 21 and older to buy marijuana from shops regulated by the state.

All three ballot initiatives are a step beyond the laws that have legalized marijuana for medical purposes. Starting with California in 1996, the District and 17 states, including the three with these ballot proposals, have passed laws making it legal to manufacture, distribute and possess marijuana for such purposes. Arkansas has a similar measure on the ballot this year.

In 2009, David Ogden, then the deputy attorney general, wrote a memo to U.S. attorneys, advising that the prosecution of significant traffickers of illegal drugs, including marijuana, remained a core priority. Marijuana distribution was the largest source of revenue for the Mexican cartels, Ogden said.

But he also addressed the growing number of states legalizing marijuana for medicinal purposes.

“Prosecution of individuals with cancer or other serious illnesses who use marijuana as part of a recommended treatment regimen consistent with applicable state law, or those caregivers . . .who provide such individuals with marijuana, is unlikely to be an efficient use of limited federal resources,” Ogden wrote.

Last year, in a memo to U.S. attorneys, Deputy Attorney General James M. Cole reiterated Ogden’s position on medical marijuana but indicated that there was a growing increase in scope of commercial cultivation, sale, distribution and use of marijuana for “purported medical purposes.”

“The Ogden Memorandum was never intended to shield such activities from federal enforcement action and prosecution, even when those activities purport to comply with state law,” Cole wrote.

In recent months, federal authorities have cracked down on the sale of marijuana from dispensaries near schools.

The DEA warned in August that about two dozen marijuana dispensaries operating in school zones in Washington state would face possible prosecution if they didn’t shut down. That same month, U.S. Attorney John Walsh in Colorado sent out 10 letters to medical marijuana dispensaries within 1,000 feet of schools, ordering them to close.